Protein malfolding plays an important role neurodegenerative conditions, such as Parkinson's Disease, Alzheimer's Disease and Motor Neuron Disease. Accumulating evidence suggests that environmental agents may contribute to the pathophysiology of these common disorders by perturbing protein folding, either directly or indirectly through their effects on cell metabolism. However, little is known about how cells adapt to the threat of environmentally-induced proteotoxicity. This study will exploit arsenic as a model for an environmental toxin that adversely affects protein folding and one that represents an important public health hazard affecting multiple organ systems. Two recently-identified adaptations to arsenic exposure will serve as this study's point of departure: (1) Regulated attenuation of new protein synthesis. (2) Modification of the cell's protein degradation apparatus to better accommodate it to arsenic-induced proteotoxicity. Stress-induced phosphorylation of translation initiation factor 2a (elF2a) attenuates protein synthesis and activates a salubrious gene expression program known as the Integrated Stress Response (ISR), which reduces the stress caused by arsenic-induced protein malfolding. Therefore, elF2a phosphorylation has emerged as an important component of cellular unfolded protein responses (UPR). Phosphatases that dephosphorylate elF2a will be characterized in an effort to identify specific biochemical steps whose inhibition activates the ISR. The physiological significance of inhibiting elF2a phosphatases will be tested in mouse models of neurodegenerative diseases. These studies will uncover the promise and potential limitations of therapeutic strategies to protect against proteotoxicity by inhibiting elF2a phosphatases. AIRAP, a novel arsenite induced protein, adapts the proteasome's regulatory cap to the conditions in cells experiencing arsenite-induced proteotoxicity and thereby promotes the cell's ability to deal with malfolded proteins. In an effort to understand how the intracellular protein degradation machinery adapts to proteotoxicity, arsenite-induced and AIRAP-dependent changes in the composition of the proteasome will be characterized by proteomic approaches. Gene knock out experiments in mouse and worms will be used to create experimental systems lacking AIRAP, and these will be applied as tools to identify arsenite-modified proteins whose degradation depends on AIRAP induction and AIRAP integration into the 19S proteasome regulatory particle. In vitro biochemical assays of purified proteasomes containing AIRAP will be used to characterize functionally proteasomal adaptation to environmentally-induced protein malfolding. The goal of this research program is to reduce the cellular adaptations to protein malfolding induced by environmental toxins to their molecular constituents. This will lay the groundwork for identifying relevant bio- markers of exposure and for future preventive and therapeutic interventions against neurodegeneration.